1. Field of the Invention
The present invention relates generally to ultra-wideband communication systems, and, in particular, to a ternary analog-to-digital converter for use in an ultra-wideband communication system.
2. Description of the Related Art
In general, in the descriptions that follow, we will italicize the first occurrence of each special term of art, which should be familiar to those skilled in the art of ultra-wideband (“UWB”) communication systems. In addition, when we first introduce a term that we believe to be new or that we will use in a context that we believe to be new, we will bold the term and provide the definition that we intend to apply to that term. In addition, throughout this description, we will sometimes use the terms assert and negate when referring to the rendering of a signal, signal flag, status bit, or similar apparatus into its logically true or logically false state, respectively, and the term toggle to indicate the logical inversion of a signal from one logical state to the other. Alternatively, we may refer to the mutually exclusive boolean states as logic_0 and logic_1. Of course, as is well know, consistent system operation can be obtained by reversing the logic sense of all such signals, such that signals described herein as logically true become logically false and vice versa. Furthermore, it is of no relevance in such systems which specific voltage levels are selected to represent each of the logic states.
Generally, in an ultra-wideband (“UWB”) communication system, a series of special processing steps are performed by a UWB transmitter to prepare payload data for transmission via a packet-based UWB channel. Upon reception, a corresponding series of reversing steps are performed by a UWB receiver to recover the data payload. Details of both series of processing steps are fully described in IEEE Standards 802.15.4 (“802.15.4”) and 802.15.4a (“802.15.4a”), copies of which are submitted herewith and which are expressly incorporated herein in their entirety by reference. As is known, these Standards describe required functions of both the transmit and receive portions of the system, but specific implementation details only of the transmit portion of the system, leaving to implementers the choice of how to implement the receive portion.
One of us, Michael McLaughlin, has developed certain improvements for use in UWB communication systems, which improvements are fully described in the following pending applications or issued patents, all of which are expressly incorporated herein in their entirety:
“A Method and Apparatus for Generating Codewords”, application Ser. No. 11/309,221, filed 13 Jul. 2006;
“A Method and Apparatus for Generating Codewords”, application Ser. No. 11/309,222, filed 13 Jul. 2006, now abandoned;
“A Method and Apparatus for Transmitting and Receiving Convolutionally Coded Data”, U.S. Pat. No. 7,636,397, issued 22 Dec. 2009; and
“A Method and Apparatus for Transmitting and Receiving Convolutionally Coded Data”, application Ser. No. 12/590,124, filed 3 Nov. 2009.
Some of us have participated in the development of certain improvements in a receiver for use in UWB communication systems, which improvements are fully described in the following pending application, which is expressly incorporated herein in its entirety:
“A Receiver for Use in an Ultra-Wideband Communication System”, application Ser. No. 12/885,517 , filed 19 Sep. 2010 (“Related Application”).
A problem of particular note in these spread-spectrum systems is a natural tension between simplicity, low power, and performance. Within the context of a spread-spectrum system, support for the above mentioned 802.15.4a standard is premised upon the ability to quickly and accurately convert the transmitted analog signal to a corresponding digital equivalent for processing, and at the same time minimizing the overall size and power of the associated circuitry. This desire for reduced area and power would naturally lead to quantizing as coarsely as the desired performance will permit. While it has been proposed to implement the front-end of a spread-spectrum receiver using a fast, 1-bit analog-to-data converter (“ADC”) to reduce the size (in terms of transistor count) of the convolution logic in both the channel impulse response (“CIR”) estimator and the channel matched filter (“CMF”), such implementations are known to be particularly sensitive to continuous-wave (“CW”) interference. This CW interference can be substantially rejected using a full 2-bit, sign+magnitude implementation such as that described by F. Amoroso in “Adaptive A/D Converter to Suppress CW Interference in DSPN Spread-Spectrum Communications”, IEEE Trans. on Communications, vol. COM-31, No. 10, October 1983, pp. 1117-1123 (“Amoroso83”), a copy of which is submitted herewith and which is expressly incorporated herein in its entirety by reference.
We have noted that, in a system adapted to quantize in units of binary digits or bits, such as that described in Amoroso83, having dual representations of the 0-state, i.e., [−0, +0], tends to increase system entropy, resulting in less-than-optimal circuit/power efficiency. One possible solution would be to implement a system adapted to quantize in units of ternary digits or trits, such as that used in a pair of obscure computers built in the Soviet Union many years ago. See, “A Visit to Computation Centers in the Soviet Union,” Comm. of the ACM, 1959, pp. 8-20; and “Soviet Computer Technology—1959”, Comm. of the ACM, 1960, pp. 131-166; copies of which are submitted herewith and which are expressly incorporated herein in their entirety by reference. Unfortunately, today (as was the case in these old machines), the available circuit technology is unable efficiently to represent and manipulate trits per se.
We submit that what is needed is an improved method and apparatus for use in the receiver of a UWB communication system for performing the analog-to-digital conversion. In particular, we submit that such a method and apparatus should provide performance generally comparable to the best prior art techniques while requiring less circuitry and consuming less power than known implementations of such prior art techniques.